Tank for holding fluids



Aug. 10, 1965 c. M. HOVEY TANK FOR HOLDING FLUIDS Filed Nov. 8, 1961United States Patent 3,199,710 TANK EEfiLDlNG FLUIDS Charles M. liovey,Winnipeg, Manitoba, Canada, assignor to Bristol Acre-industries Limited,Montreal North, Quehcc, Canada, a corporation of Canada File-d Nov. 8,1961,3212 No. 150,936 Claims priority, application Canada, Oct. 3, 1961,332595 5 Claims. (Cl. 22tl-1) The present invention relates to anelongated cylindrical tank having an open upper surface.

Tanks of the type under consideration are normally formed by assemblingtogether a plurality of individual flat plate members such as by weldingand supporting these members on a frame designed to resist the outwardand downward loads imposed on the tank by its contents. Normally, suchtanks are provided with bracing members across the upper surface of thetank to resist the tendency of the sides to move outward away from oneanother. Where such tanks are very long, it is normally impossible toconstruct the tank without some form of cross bracing across the uppersurface.

Tanks of this sort are often used for electro plating or other chemicalbath processes. The solutions normally contained within these tanks mayattack the materials from which the tanks are constructed, such as steeland aluminum, and accordingly it is necessary to line the interior ofthese tanks to prevent the corrosion of the walls and the bottom. Itwill be appreciated that the protection of the interior of a tank wallappreciably adds to the over-all weight which the supporting structureis called upon to carry, as well as adding to the cost and complexity ofmanufacture.

Tank structures, in accordance with the teachings of the prior art, havenormally been constructed at a location remote from the place where theyare used, and it is frequently necessary to knock out the wall of abuilding to locate the finished tank in its working position.

The present invention overcomes the shortcomings of known tankstructures by providing a tank which has only tensile stresses in itswall. Accordingly, there is no tendency for the walls of such a tank todeflect outwardly and there is no necessity to provide cross bracingover the top of the tank. Since only tensile stresses occur in the wallsof the tank, the walls may be made of thin material, and where platingbaths or other chemical solutions are contained in the tank, it becomespracticable to construct the walls of the tank from a non-corrosivemetal. Further, since the wall of such a tank are subjected to tensilestresses only, these walls may be made very thin so that the wallstructure of the tank may be carried within a plant as a rolled sheet ofmaterial and then assembled to the supporting structure to form thefinished tank. It will be appreciated that a considerable saving in thecost of erecting a large tank will result where there is no necessity toremove the wall from a building in order to get the tank inside. Thesupporting structure for such a tank will similarly be much smaller andlighter than the supporting structure for a corresponding tankconstructed in accordance with the teachings of the prior art.

The present invention provides a hollow frusto-cylindrical tank having across section orthogonal to its axis with a radius of curvature at apoint on said cross section inversely proportional to the depth of saidpoint below the surface of a liquid in said tank. Such a tank mayreadily be supported by a pair of support members extendinglongitudinally of the tank and fixed to the wall thereof at the freeupper edges. There is no necessity to provide any cross bracing in sucha tank, since the forces exerted on the walls of such a tank are tensileonly. Accordingly, it is only necessary to provide supports which maycarry a load directed tangentially to the upper edge of the Wall of thetank.

The invention further provides a hollow frusto-cylindrical tank having apair of end walls, a continuous side and bottom structure, a pair ofhorizontal members adapted to support said side and bottom structure atthe upper edges thereof, said side and bottom structure being formed ofa single sheet of material and having a cross section orthogonal to theaxis of the cylinder with a radius of curvature at any point on saidcross section inversely proportional to the depth of the point below thesurface of a liquid in said tank.

A tank structure in accordance with the present invention may have across section shape defined by the diiferential equation:

where T is the tensile force in the wall per unit of tank length, where7 is the specific weight of the contained liquid, y is the depth belowthe free surface of the liquid to a point on the tank, and x is thehorizontal distance to said point from the vertical axis of symmetry ofthe tank corresponding to the distance y below the surface of theliquid.

In drawings which illustrate an embodiment of the invention:

FIGURE 1 is a perspective view of a tank structure in accordance withthe present invention; and

FIGURE 2 is a cross section of such a tank.

As shown in FIGURE 1, a tank 10 is provided with a continuous sheet wallsurface 11 supported by the horizontal rails 12 and 13 fixed to the wallstructure 11 by means (not shown). The rails 12 and 13 are shownsupported on legs 14, 15 and 16. These legs are directed to be in linewith a tangent of the curvature of the tank wall at the upper edge ofthe wall. The tank is provided with ends 17 and 18 to form the completedtank. As shown, end 17 is formed with a plurality of ribs 1? which serveto stiffen the ends of the tank.

As shown in FIGURE 2, the radius of curvature R of the tank variesthroughout the depth h of the tank. The tank being symmetrical about theaxis 29. In accordance with the invention, the radius of curvature R ata point 21 on the surface of the tank is inversely proportional to thedistance 11 of the point 21 below the surface of the liquid contained inthe tank. Expressed mathematically: IzR=K, where K is a constant. Also,it will be appreciated that by varying the value of K and the positionsof the support rails and the ends 17 and 18 of the tank, that tanks ofdifferent depths and Widths can be formed.

Such a tank is characterized by the feature that the only forcesexisting in the wall of the tank are tensile forces and there are noforces directed other than in the plane of the walls.

Accordingly, the tank as described may readily be constructed ofmaterial which is much thinner than materials previously used. Forexample, a steel tank 3 feet in depth which might be used in electroplating need have a wall thickness of only 0.001 inch in order tosupport the plating solution. More usually, though, such a tank would beformed of 0.020 inch to give a safety factor.

Because of the use of very thin sheet to construct the tank, it becomeseconomically feasible to manufacture tanks from stainless steel,titanium or other expensive alloys. Such alloys have special propertieswhich enable them to resist the corrosive action of specific liquids. Inconventional design, the weight of material required is so high that thecost may be prohibitive. In some cases, heavy steel tanks are lined orclad with a thin layer of expensive corrosion-resistant material. Thenew tank design eliminates the necessity for a heavy rigid supportingstructure and is therefore less expensive.

The wall of the tank is so thin that it can frequently be fabricatedflat. For example, a tank thirty-nine feet long and ten feet wide can bemade by welding thirteen 3 x 20 strips together to make a fiat sheet 39'x 20.

Tank ends and the supporting structure can be built separately. Thelarge sheet can be rolled up like paper and can be carried along withthe tank ends and supporting structural members through a normal sizeddoorway into the building where it is to be used. A simple assembly jobcompletes the tank. In this way, very large tanks may be produced at amanufacturers plant and shipped to the consumer, Whereas a conventionaltanks would have to be constructed at the users site.

In many cases, brick walls must be torn down in order to place largetanks in the users premises. The present invention eliminates thisrequirement.

A most important aspect of the tank is that it may be made so that itssides are nearly vertical at the top. Such a tank needs no horizontaltie-bars to prevent the sides from bulging outwards. A tank of greatlength can be constructed using the same thickness of material whichwould be required for a short one. Such a tank is very useful in theelectroplating industry where horizontal tiebars would prevent longarticles from being placed in and removed from the tank.

Another advantage is that the tank, having no corners, is very easilycleaned.

As previously mentioned, the differential equation describing the crosssection of a tank constructed in accordance with the present inventionmay be written as follows:

hen" Where T is the tensile force in the wall of the tank per unit oftank length; 7 is the specified weight of the contained liquid, and y isthe depth (previously referred to as h) below the free surface of theliquid. The radius of curvature are =T/'yy in the above equation.

From FIGURE 2 it is evident that the tank has boundaries and that thevalues thereof may be expressed as follows:

At x=0, 3 :11 (the maximum depth at tank centreline) At y=0, x= /2 tanktop width At y=0, R=oo At x=0, dyldx= wherein R refers to the radius ofcurvature of the tank and is equal to T/y. The indication that R becomesinfinite at y=O provides for the tank shape becoming a straight linebeginning at and above the x axis (a horizontal line coinciding with theillustrated liquid surface) as shown in FIGURE 2. Of course the lastboundary value set forth above means the slope of the tank structure atits bottom is zero when x=0.

The equation above is the differential equation of the curve of the tankprofile. This equation has not yet been solved to give a directalgebraic equation. A solution by successive approximation has beenderived by means of which tanks can be conveniently designed.

For comparison, the algebraic and differential equa- 4 tions of theparabola and catenary are given as follows. It is readily seen thatthese are quite different from the above one.

Parabola:

Algebraic =2 Differential P Catenary:

a a: x Algebraic y-. -2 4-73 Differential I claim: 7

1. An open top tank for holding a given liquid to a predetermined freesurface level, comprising:

a pair of end walls,

a continuous side and bottom structure having a pair of longitudinalupper edges,

means secured to said edges for supporting said side and bottomstructure only at the said upper edges thereof,

said side and bottom structure being formed of a sheet of materialextending between said end Walls and having orthogonal to thelongitudinal axis of the tank a cross section with such a radius ofcurvature from the said liquid level downward that any point on saidcross section is inversely proportional to the depth of the point belowthe said predetermined liquid surface level to cause a substantiallyconstant tensile force in said structure per unit of tank length and tocause in conjunction with said supporting means substantially a zerotransverse force in said structure at each of said upper edges.

2. A tank as in claim 1 wherein said supporting means includes a pair ofhorizontal members respectively extending lengthwise of said edges.

3. A tank as in claim 2 including in said supporting means a pluralityof legs for supporting said horiozntal members.

4. A tank as in claim 1 wherein the said cross section is defined in avertical plane by the equation lzR=-K, wherein it is the aforesaid depthof a point on the cross section below the liquid level, R is the saidradius of curvature at said point, and K is a constant including thesaid tensile force per unit of tank length.

5. A tank as in claim 4 wherein the said K=T'y, T being the saidconstant tensile force in the wall structure per unit of tank length,and 7 being a constant representing the specific Weight of the saidgiven liquid, the horizontal force in said structure at h=0 beingsubstantially zero.

References Cited by the Examiner UNITED STATES PATENTS 625,947 5/99Berquist. 935,943 10/09 Stoelting 220-1 FOREIGN PATENTS 1,031,067 5/58Germany.

751,736 7/56 Great Britain.

THERON E. CONDON, Primary Examiner.

EARLE I. DRUMMOND, GEORGE O. RALSTON,

Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,199,710 August 10, 1965 Charles M. Hovey It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 4, lines 11 and 12, the equation should appear as shown belowinstead of as in the patent:

same column 4, lines 14 and 15, the equation should appear as shownbelow instead of as in the patent:

Signed and sealed this 3rd day of May 1966.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

1. AN OPEN TOP TANK FOR HOLDING A GIVEN LIQUID TO A PREDERERMINED FREESURFACE LEVEL, COMPRISING; A PAIR OF END WALLS, A CONTINUOUS SIDE ANDBOTTOM STRUCTURE HAVING A PAIR OF LONGITUDINAL UPPER EDGES, MEANSSECURED TO SAID EDGES FOR SUPPORTING SAID SIDE AND BOTTOM STRUCTURE ONLYAT THE SAID UPPER EDGES THEREOF, SAID SIDE AND BOTTOM STRUCTURE BEINGFORMED OF A SHEET OF MATERIAL EXTENDING BETWEEN SAID END WALLS ANDHAVING ORTHORGONAL TO THE LONGITUDINAL AXIS OF THE TANK A CROSS SECTIONWITH SUCH A RADIUS OF CURVATURE FROM THE SAID LIQUID LEVEL DOWNWARD THATANY POINT ON SAID CROSS SECTION IS INVERSELY PROPORTIONAL TO THE DEPTHOF THE POINT BELOW THE SAID PREDERERMINED LIQUID SURFACE LEVEL TO CAUSEA SUBSTANTIALLY CONSTANT TENSILE FORCE IN SAID STRUCTURE PER UNIT OFTANK LENGTH AND TO CAUSE IN CONJUNCTION WITH SAID SUPPORTIN MEANSSUBSTANTIALLY A ZERO TRANSVERSE FORCE IN SAID STRUCTURE AT EACH OF SAIDUPPER EDGES.